Known asset location and recovery systems typically provide a specialized locating device ‘LD’ to be associated with an asset such as a motor vehicle which a user, i.e. an ALSP subscriber, may wish to attempt to recover should it be moved without the user's permission, e.g. stolen. In the case of motor vehicles where this technology is best known, the LD is normally located at a secret location within the motor vehicle or at least in or at a part of the vehicle which is not easily accessible without undue effort. Placing the LD at a secret or difficult to access location is intended to prevent a thief from removing and discarding the LD from the asset during the course of stealing it. Preferably, the thief will not realize that the asset has a LD attached to it.
Some known asset locating and recovery systems enable the LD to use a public mobile radio network ‘PMRN’ such as a global system for mobile telecommunications system ‘GSM’ to communicate with an operations control centre ‘OCC’ which is sometimes referred to as a customer service centre ‘CSC’ or command and control centre ‘CCC’. The OCC is the management centre which manages subscribers and which controls asset location and recovery when a report or alert is received that an asset has been stolen, etc. A problem with such an asset location system is that PMRN coverage is not determined by the needs of the ALSP, but instead by the needs of the PMRN operator for its normal mobile radio network subscribers. Consequently, there may be areas within a PMRN with no or poor network coverage or signal reception and these areas may comprise locations where the ALSP requires the ability to transmit to or receive signals from a LD in order to activate, track and locate it once an alert is triggered.
Furthermore, because LDs are normally located in secret or difficult to access locations, thieves often attempt to deliberately jam local PMRN transmissions. Localized PMRN jammers are readily available at inexpensive prices in many countries; even in countries where the use or ownership of such jammers is illegal. If a thief uses such a jammer in close proximity to a LD, it means that, even when the LD in a stolen asset can receive GPS satellite information and determine from the GPS signals its own location, it cannot transmit its GPS location information to an OCC over the PMRN thus rendering the LD ineffective and thereby making stolen asset recovery inefficient or even impossible.
The logical solution to the coverage and jamming problems faced when using a PMRN for communication in an asset location and recovery system is for an ALSP to use a private radio frequency network ‘PRFN’ and, in fact, this is what many ALSPs do. A PRFN is controlled and operated by the ALSP for only its subscribers and is unlikely to encounter lack of coverage/signal reception issues in the same locations as PMRNs because the ALSP can select where to provide coverage by installing suitable PRFN equipment at appropriate locations according to its own criteria relevant to the nature of the asset requiring protection and the historical experience of its theft or loss. Furthermore, a PRFN does not present the same issues for an ALSP as a PMRN in terms of jamming in that it is much less likely for off the shelf jamming devices to be available to jam a private radio frequency ‘PRF’. Furthermore, the transmitter power required of a jammer for jamming high power base station RF transmissions and lower power LD RF transmissions on a PRFN is high. It is difficult to maintain this level of power transmission consistently without expensive, heavy duty equipment and it would be a challenge to use such equipment in a time-sensitive mobile environment such as an asset theft situation. Also, because of the high power needed for jamming, if thieves do attempt to jam the transmission frequency on a PRFN, the ALSP is able to use direction finding techniques to track on the signal generated by the jamming, equipment which defeats the purpose of jamming by assisting in asset location and recovery.
A downside, however, is that deploying a PRFN requires significant capital expenditure in that it necessitates the building and operating of a dedicated network of radio base stations with sufficient density to transmit signals to, and receive signals from, the low power radio transmitter-receivers in LDs of subscriber assets within the ALSP region of operation. The region of operation may be geographically very large and therefore require a considerable number of base stations to be installed. Also, the costs of operating the PRFN are affected by many other factors not encountered by an ALSP with PMRN use such as site rental costs for hardware such as base stations, power and maintenance costs, and software licences.
Some known asset location and recovery systems enable the LDs to receive global positioning system signals in order to determine their GPS locations and report these to the OCC, for example. In certain situations, however, a GPS receiver system in an LD is unable to receive signals from a sufficient number of GPS satellites for the LD to be able to calculate its GPS location. Also, there are many commercially available GPS jammer products that are specifically designed to prevent the reception of the GPS signals that are used to locate assets.